Never had a problem with the run-of-the-mill replacement brands recommended at the auto parts store. Typically they're less than half the cost of AC Delco injectors. The disclaimer is that while I've swapped out dozens of them, and never had a failure, it certainly could happen with cheaper parts (more likely than AC Delco). Also, I've not ever replaced injectors for or in high performance applications.

When you buy replacement injectors, the new ones should have O-rings. Open the box before you leave the auto-parts store, to be sure.

As a rule, you should always replace O-rings if the injector is removed from the rail or engine. Again, even remove the fuel rail from injectors not being replaced, you should go ahead and replace the O-rings (they're really cheap... a few pennies a ring up to about $1 a set of 2). Rings harden over time, and removal from the rail/engine results in microfracturing. Even new rings can have fracturing occur, hence the need for lubrication. You may not see the splits, but if formed, they can widen over time, and cause leaking. Leaking fuel into the engine compartment or engine is typically far more costly than a buck or two for new o-rings!

When replacing your o-rings, lubricate them with clean motor oil before putting on the injector, and definitely before putting into the fuel rail. The motor oil (or even vasoline/petroleum jelly works as the ring material is designed to NOT deteriorate when exposed to petroleum products) is applied to prevent microfracturing during insertion/connection to the engine/rails. Splits and fractures may not be apparent, so don't trust your eyes. Last thing you need is to have fuel leaking from your rail at high temp and being exposed to any kind of spark (fire in the engine compartment isn't fun!). Definitely worth the cost of replacement during maintenance.

Also, I've found if you don't have the tools to depressurize the fuel lines, you can use the vehicle's fuel safety cut-off switch to your advantage. The switch is usually under a kick panel in the cab, though you should check your owner's manual for specifics.The cut-off switch is designed to engage in an accident/roll-over to prevent fuel from being sprayed everywhere if the lines are damaged. Pull the plug, the fuel pump becomes inoperable. By pulling the plug and disengaging the fuel pump, you can then turn over the engine a few times to consume the fuel in the pressurized lines. The result is the elimination of line pressure. Pulling a fuel line will do the same, but be aware the fuel will spray EVERYWHERE when you do it, because it's under pressure!

Regardless the method you choose, make sure you relieve line pressure before removing the fuel rails. Spraying fuel into the engine compartment isn't a safe thing to do. If you find you spill a decent amount of fuel anyway (very common, even with unpressurized lines), wipe up what you can and allow the rest to evaporate for a few minutes before continuing. A spark with gasoline fumes isn't a pleasant experience.

Do this job in a well ventilated area, as well.

Lastly, I recommend doing this on a COLD engine. It's just more pleasant to work on when you're not burning your hands from the engine heat!